This invention relates to a vertical stepper for transferring a circuit pattern formed on a mask by using synchrotron radiation (hereinafter simply referred to as "SR") as a light source.
In recent years, attention has been paid to an X-ray exposing method as means for manufacturing memory devices as VLSI of 16M bits or more which employs SR instead of a light source. This exposing method has features such as the wavelength of the light source is short and its parallel property is good compared with the conventional exposing method in which an ultraviolet (UV) ray is used. As a result this method is not only suitable to be used for transferring a submicron pattern of but also a high throughput can be expected because the strength of SR is large compared to UV radiation and thus exposure time is less.
As a conventional exposing device for VLSI, there has been known a horizontal stepper (reduced projection exposing device) using an ultraviolet ray. This horizontal stepper is designed such that a wafer and a mask are horizontally disposed at a predetermined space, and an ultraviolet ray is irradiated from a light source disposed above in order to transfer a circuit pattern formed on the mask onto the wafer in a reduced scale. However, such ultraviolet ray exposure type horizontal stepper has such disadvantage in that the wavelength of the ultraviolet ray is too long, it is not suitable to the exposure of a circuit pattern of submicron dimensions. This is the reason why the above-mentioned X-ray exposing method using SR instead of a light source draws much attention as means for manufacturing VLSI memories of 16M bits or more.
FIG. 1 illustrates a schematic view showing the principle of generating SR. Electrons accelerated by an accelerator (not shown) and made incident to a storage ring 1 are circulated within the vacuum storage ring 1 while being bent in orbit by a deflection magnet 2. A beam-like SR 3 is irradiated in the tangent direction from the portion of the storage ring 1 where the electron orbit is bent by the deflection magnet 2. Though this SR 3 includes a wide range of wavelengths of electromagnetic waves such as from an ultraviolet ray to an X-ray, an X-ray of a predetermined range of wavelengths is obtained by cutting such electromagnetic waves with other wavelengths by using mirrors, a Be-window, etc. (not shown) and the thus obtained X-ray is used for exposure.
By the way, in order to generate SR, it is necessary that electrons are accelerated from approximately several hundred MeV to approximately several GeV. In order to meet this requirement, the SR generator must be large in size compared to a UV lamp and therefore the SR generator must be horizontally installed. In this case, as SR is irradiated in the horizontal direction, a stepper using SR for exposure is necessarily of a vertical type wherein the mask and the wafer are vertically oriented.
Also, SR 3 has a rectangular shape in section elongated in the horizontal direction as shown in FIG. 2. Therefore, since a single scanning is not enough to cover the whole exposing area 4 on the mask, it is required to perform a vertical scanning wherein the mask and the wafer are integrally moved in the vertical direction during exposure. Furthermore, the whole surface of the wafer is required to be exposed by moving the wafer through a step-and-repeat action in the same manner as the conventional horizontal stepper wherein a visible ray, an ultraviolet ray, etc. are used as exposure radiation.